Variable electrical condenser



Jan. 12, 1932. H. AND EWES' 1,840,298

VARIABLE ELECTRICAL C ONDENSER Original Filed Aug. 21, 1925 man I @mmuu 7 INVENTOR "(IMF 2E Y A/VDPfWE-s 1 BY I I5 7 ATTORNEYS Patented Jan. 12,1932

HUMFREY'ANDREW'ES, OF HIGHGATE, LONDON, ENGLAND VARIABLE ELECTRICAL CONDENSER Application filed August 21, 1925, Serial No. 51,606', and in Great Britain October This invention relates to electrical devices such as variable electrostatic condensers and '0 variable inductances and has for its objectthe provision of an improved form of coni denser (or inductance) or an attachment for a condenser (or inductance) which is particularly suitable for tuning two circuits simultaneously. v The invention is more particularly concerned with variable condensers (or induetances) of the type which comprise two similar parts coupled together in such a manner that the capacities (or inductances) of the,

parts can be simultaneously and correspondingly varied from a maximum value to a minlmum value and are sometimes employed for tuning in the case of multi-stage high frequency amplifiers.

One of the difiiculties which is frequently g0 encountered in the simultaneous tuning of two circuits by the use of a double or two-part condenser (or inductance) is that it is very difiicult to secure exact equality in the constants of the two circuits. For example in the case of a two-part condenser consisting of a plurality of interleaved fixed and movable plates of substantiall semi-circular formation and provided wit means for simultaneously varying the capacity of the two parts, although t e two parts may have been manufactured un er identical conditions and consist of equal numbers of fixed and movable plates spaced apart to the same extent in each condenser part, it is very rare that the two parts are found to have identically the same capacities for all positions of the movable plates or even if the two parts have identical capacities it is very rare that the two parts when connected in circuit produce exactly the same electrical effects in the two circuits. Amongst other reasons this inequality of the constants of the two circuits may be due to imperfections in the manufacture or assembly of the parts, appurtenances or other apparatus with which the parts co-operate, or the employment of different lengths of wiring for connecting the parts, appurtenances or other apparatus in circuit and it is the object of the present invention to provide means for compensating for such inequalities there- I August 28, 1824. Renewed 2, 1930. r

by overcoming the difficulty above referred The invention consists in an electrical device having members upon the relative position of which the electrical characteristics of the device depend, adapted to be associated with a pair of condensers or a two-part condenser (or inductance) in such a manner that when relative movement is caused to take place between the said members as much capacity {or inductance) is added to one condenser, inductance or part as is subtracted from the other condenser, inductance or part. i

. The invention also consists in means whereby a pair of condensers (or inductances) or two parts of a condenser (or' inductance) may be caused to have the same capacity (or (or inductances) inductance) or in combination with other electrical apparatus or appurtenances may be caused to produce the same electrical efi'ect 1n operation, comprising an auxiliary variable condenser (or inductance) which isv adapted to be electrically connected up with the pairiof condensers (or inductances) or the two parts of a condenser (or inductance) in such a manner that when relative move-,

ment is caused to take place between the elemerits of the auxiliary condenser (or inductance as much capacity (or inductance) is adde to one condenser, inductance or part as is subtracted from the other condenser, inductance or part.

Further features of the invention will be hereinafter described and delimited-in the appended claims.

Referring now to the accompanying drawings which illustrate by way of example, two convenient modes of carrying the invention into effect Figure 1 shows one view of a two-part condenser embodying the invention;

Figure 2 is a sectional plan view taken on line 22 of Figure 1,

Figure 3 is a and diagrammatic view illustrating'the application of the invention to inductances.

In Figures 1 and 2 of the accompanying drawings the invention is shown as applied to a two-part condenser each .part of which is made up of a plurality of alternately arranged fixedand movable plates of substantially semi-circular formation. The movable plates of each part are mounted upon a common operating spindle 1 so that the movable plates 2 of one part of the condenser are disposed on one side of a vertical plane contain ing the axis of the operating spindle and the movable plates 3 of the other part are disosed on the other side of such plane that is to say, the plates 2 are displaced through an angle of180 in plan view relatively to the plates 3. The fixed plates of one part are similarly arranged with respect to the fixed plates of the other part so that the capacity of one part is at a maximum when that of the other part is at a maximum and the capacities of the two parts can be correspondingly and simultaneously varied by the aid of an operating knob 4 which is rigidly connected to the spindle 1.

In carrying the invention into effect as applied to a two-part condenser of the type above described, an auxiliary condenser consisting of at least one substantially semi-circular movable plate 5 and two substantially semi-circular fixed plates 6 and 7 is associated with the two-part condenser in such a manner that one fixed plate of the auxiliary condenser overlies the fixed plates of one of the condenser parts and the other fixed plate of the auxiliary condenser overlies the fixed plates of the other condenser part, the two fixed plates 6 and 7 being arranged in the same plane with their straight edges parallel.

The movable plate 5 is rigidly secured to an operating spindle 8 provided with an operating knob 9. As shown the operating spin dle 1 is made hollow to allow the operating spindle 8 of the auxiliary condenser to pass freely therethrough. Normally the movable plate 5 will occupy the position shown in drawings, that is to say it will overlie each of the fixed plates 6 and 7 to an equal extent. In this position of the movable plate 5 equal amounts of additional capacity are added to each of the main condenser parts by the auxiliary condenser; when the latter is connected up with. the main condenser in the manner illustrated with the fixed plates of the auxiliar condenser electrically connected to the fixed. plates of the main condenser parts, by rotating the knob 9 the movable plate 5 is caused to move across the fixed plates 6 and 7 so that as much capacity is added to one partof the main condenser as is subtracted from. the other part. Thus the auxiliary condenser acts as a balancing device to equalize the capacities of or the electrical effects in the two circuits in which the condensers are connected so that the two circuits may be simultaneously tuned withextreme accuracy.

Any convenient arrangement of terminal members may be employed; for example, as indicated in. dotted lines in Figure 2 of the drawings three terminal members 11, 12 and 13 may be employed, one of which (say 11) is electrically connected up with the fixed plates of one condenser part and with one of the fixed plates (say 6) of the auxiliary condenser, another of which (say 12) is electrically connected up with the fixed plates of the other condenser part and with the other fixed plate (say 7) of the auxiliary condenser and the third (say 13) is electrically c0nnected up with the movable plates of both condenser parts and with the movable plate of the auxiliary condenser.

In order' to electrically connect the fixed plates of the auxiliary condenser with the respective sets of fixed plates of the condenser parts, the posts for supporting the fixed plates of the main condenser in their appropriate positions may be provided with extensions on which plates 6 and 7 may be mounted, or if desired the auxiliary condenser may be secured to the main condenser in such a manner that the binding posts of the auxiliary condenser contact with the binding posts of the main condenser.

In Figure 3 of the accompanying drawings there'is diagrammatically illustrated one convenient form of inductance attachment or balancing device produced in accordance with the invention which may be mounted on or connected up with a variable inductance consisting of two similar parts adapted to be correspondingly and simultaneously varied from a maximum to a minimum value. In this form the device consists of three D- shaped inductance members, two of which ('14 and 15) are fixed in the same plane so that one is electrically connected with the fixed member (or members) of one inductance part, and the other is electrically connected with the fixed member (or members) of the other inductance part The third D-shaped inductance member 16 is arranged so as to be capable of being moved across the two fixed members 14 and 15 in such a manner that when the member 16 is displaced from its midposition (i. e.. the position in which it is shown in the figure) as much inductance is added to the one inductance part as is subtracted from the other inductance part. As illustrated the D-shaped inductance members are wound in the form of equal segments of a circle, the two fixed segmental members he- 1ng arranged with their chords parallel and disposed at equal distances from the diametrical line of the circle of which they form parts and the movable member being arranged so as to be capable of being rotated in a plane parallel to that containing the fixed members and about the centre of said circle.

It will be appreciated that the balancing device may take the form of a separate condenser (or inductance) which is adapted to be mounted upon or connected up with a twopart condenser or inductance or that it may be constructed as a c'omponent'part of a twopart condenser (or inductance) according to the wishes of the user.

It will be appreciated that by suitably modifying the apparatus above described the invention can be readily adapted for use in conjunction with a variable condenser (or inductance) having more than two parts.

While the invention in its application to variable condenser has been described as applied to variable condensers of the type built up of a plurality of alternately arranged fixed and movable plates of substantially semi-circular formation it will be understood that the invention may, if desired, be applied to variable condensers of other types possessing two or more members upon the relative positions of which the electrical capacities epend Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. The combination of a plurality of main condensers each of which is variable as to capacity, and an auxiliary condenser comprising a pair of fixed condenser elements, and a movable condenser element arranged so that the movable element can add to the effect of one of the elements of the-auxiliary condenser, while subtracting from the effect of the remainder thereof, the main condensers and the auxiliary condenser being electrically connected to operate in unison-so that the capacity of the main condenser is influenced by the auxiliary condenser.

2. The combination of a plurality of main condensers having fixed and movable plates, means for operating said movable plates in unison, and an auxiliary variable member electrically operatin in unison with said movable plates for a ding capacity to one of i the mam condensers and simultaneously subtracting the same value of capacity from another of said main condensers.

3. The combination of two main condensers having fixed and movable plates, means for operating said movable plates in unison, and an auxiliary variable condenser for adding various values of capacity to one of the main condensers and simultaneously substracting the respective values of capacit from the other main condenser, the mova le element of the auxiliary condenser being connected to operating means positioned by said means for element of said auxiliary condenser being connected to operatin means journalled within the said shaft 0 the main condenser.

5. The combination of two main condensers having fixed and movable plates, a shaft for rotating the movable plates of each main condenser in unison, and an auxiliary variable condenser having fixed and movable plates for adding various values of capacity to eitherof the main condensers and simultaneously subtracting the respective values of capacity from the other main condenser, the movable plate of said auxiliary condenser being rotatable and having operating means passing through the said shaft of the main condensers.

6. The combination of two main condensers having fixed and movable plates, means for operating said movable plates in unison, an auxiliary variable condenser having at least two fixed plates, each of said fixed plates being electrically connected to the fixed plates of one of themain condensers, respectively, the movable plate of the auxiliary condenser being electrically connected to the movable plates of the main condensers, the plates of the auxiliary condenser being adjusted so that when relative movement is caused to take place between them as much capacity is added to one of the main condensers as is subtracted from the other main condenser.

Dated this 22nd day of May, 1925.

In testimony whereof I aflix my signature.

HUMFREY ANDREWES.

operating the movable plates of the main condensers.

4. The combination of two main condensers having fixed and'movable plates, a shaft for operating said movable plates in unison, and an auxiliary variable condenser for adding various values of capacity to either of the main condensers and simultaneously subtracting the respective values of capacity from the other main condenser, the movable 

